The use of such a sliding sleeve is well known in constant-mesh gear transmissions of the synchromesh type, e.g. as described in "Principles of Automotive Vehicles", Manual TM9-8000 and TO36A-1-76, published January 1956 by the Department of the Army and the Air Force, pages 284-288. In the system described in that publication, the sleeve is in permanent mesh with a sliding gear splined to a main shaft and is releasably connected therewith for limited joint axial motion by a set of spring-loaded ball checks. The sliding gear and the coaxial gear to be driven thereby are provided with confronting frustoconical clutch surfaces which are separated by a small clearance in a decoupling position but contact each other when the first gear and its sleeve are axially moved toward a coupling position. The second gear is then frictionally entrained and accelerated (or possibly decelerated) until its speed substantially equals that of the first gear. Only then can the teeth of the sleeve enter between the teeth of the second gear, the two sets of teeth being suitably beveled at their confronting ends to facilitate the meshing engagement.
In lieu of a sliding gear it is also possible to use in such a system an axially fixed driving gear together with a so-called synchro ring coaxially interposed between the two gears, the synchro ring rotating with the driving gear but being axially entrainable by the sleeve through ball checks or the like to establish frictional contact between a clutch surface on that ring and a confronting clutch surface on the driven gear. Upon the establishment of such contact, the sleeve is released from the synchro ring and can be axially slid into engagement with the driven gear.
The completion of the shift of the sleeve into a coupling position, however, is not always smooth with either type of system and, when carried out too rapidly, could still give rise to annoying gear clashing.
The synchromesh-type gear transmission described in my copending application Ser. No. 141,150, now U.S. Pat. No. 4,390,090, effectively prevents by simple means any attempted meshing between the sleeve in permanent mesh with a first gear and a second gear to be coupled thereto until and unless the relative slip of the gears has been eliminated. For this purpose the first gear (usually the driving one) is provided with detent means in the form of several--preferably three--peripherally equispaced rocker members having feet pivotally received in the body of that gear and heads extending substantially radially under outwardly acting spring pressure into an inner peripheral recess of the sleeve in the decoupling position of the latter in which the teeth of the sleeve are not engaged with those of the second (e.g. the driven) gear. Upon an incipient axial shift of the sleeve toward that second gear, the stem of each rocker member exerts an axial thrust upon a synchro ring which is coaxially interposed between the two gears with freedom of limited rotation relative to the first gear. This axial thrust establishes frictional contact between coacting clutch surfaces of the synchro ring and the second gear whereby that ring is entrained into or maintained in a position of rotational disalignment relative to the first gear as long as a significant speed difference or slip exists between the two gears. In that disalignment position each rocker member comes to rest against one of two webs on the synchro ring by which it is bracketed, the webs and the rocker members being provided with flat camming surfaces which prevent a radial inward displacement of the rocker members until the speed difference between the two gears and thus the frictional torque resisting the depression of these members have been sufficiently reduced to enable the rotation of the synchro ring into a position of relative alignment. It is only then that the sleeve can complete the axial shift in order to establish a coupling position in which its teeth also mesh with those of the second gear. The pivotal motion of the rocker members acting as detents translates the sliding force exerted upon the sleeve into an intensified axial thrust acting on the synchro ring.
The relatively large contact area between the flat sloping camming surfaces of the detent members and the webs of the synchro ring generates considerable friction which must be overcome to establish the rotational alignment enabling a shifting of the sleeve into its coupling position. There is also additional friction between each detent member and another surface of the synchro ring which receives the axial thrust exerted by that member.